The present invention relates to a process for manufacturing a ladder of composite material, as well as the ladder obtained by said process.
It is known that recently composite materials have revolutionized construction and production technologies due to their high mechanical characteristics together with their intrinsic lightness in weight (as compared with metal materials, for example).
Application of composite materials in different technical fields is still subject to intense research and development efforts, taking into account the very wide number of composite materials that can be defined and employed in the most varied constructions.
Generally, composite materials are differentiated from each other based on the typology of the reinforcing fibers and/or the resins used as binding agents between said fibers; in more detail, it is to be noted that, for manufacturing (extruded or pultruded) section members, the employed resins are generally made of polymeric substances.
Usually, the polymeric substances employed in pultrusion processes as binding resins (for impregnation of the resistant fibers) are of the thermosetting type, i.e. they have a chemical structure that, once polymerized, if exposed to high temperatures, is submitted to an irreversible decay as regards its structure (it carbonizes, for example).
A particular application field for composite materials is found in ladder manufacture; in this production sector, the main components of a ladder (one or two upright lengths and a plurality of rungs) are usually made separately, by forming or molding for example, and they are subsequently assembled.
As far as rungs and upright lengths are concerned, different typologies are adopted by the known art which substantially aim at obtaining a rung-upright length link which can be easily disassembled and has a certain degree of stability, in view of a heavy use of the ladder. In other words, in making ladders of composite material, apart from the structural efficiency of the individual constituent elements, a very important role from the point of view of quality of the finished product and the manufacturing costs is performed by the technical and operating modalities for rung-upright length assembling.
For assembling upright lengths and rungs, the construction solutions of known type may involve the presence of one or more gluing areas or the existence of elements interposed between the rungs and the upright lengths; in other words, the known art teaches from a technical point of view how to indirectly connect rungs and upright lengths, i.e. it envisages that transmission of the mechanical actions and maintenance of the relative positions between these components should rely on an appropriate third construction element (which may be a suitably added adhesive material or a true junction element).
Although known solutions are widespread, it is to be pointed out that the above described known art has some drawbacks.
In fact, due to the necessity to use the mentioned interconnecting element, the production processes become more complicated, which will bring about an increase in the operating time.
Typically, suitably shaped seatings and coupling regions are to be created on the upright lengths and/or the rungs and these regions may be critical areas for starting of sudden yielding or yielding propagating in time within the material.
Furthermore, addition of a supplementary element to the connecting region between rungs and upright lengths (which element generally has physico-chemical characteristics different from those of the other constituent elements in ladders) gives rise to a generally heterogeneous article, having hardly-predictable problems in terms of dynamic behavior and thermal deformation.
In addition, a drawback directly affecting the operating times and costs is given by the fact that thermosetting resins have some working problems, exactly because they are exposed to particular work conditions (specifically, very hot heat sources); this adversely affects the structural integrity of the ladder, since the binding resin does not fully carry out packing of the mechanically resistant fibers and can give rise to breaking, separation or presence of intolerable backlashes between rungs and upright lengths.
In the light of the above, it is a fundamental aim of the present invention to manufacture a ladder of composite material capable of substantially eliminating the above discussed drawbacks.
In particular, it is an object of the present invention to provide a process for manufacturing ladders of composite material adapted to greatly reduce the manufacturing difficulties, with clear benefits in terms of time and production economy.
In addition, the present invention aims at devising a production process capable of manufacturing a ladder of simplified structure, which at the same time has excellent solidity and steadiness features.
It is a further object of the invention to provide a production process enabling manufacture of a ladder of composite material without running into the mentioned working problems typical of thermosetting resins, and in particular capable of avoiding decay of the binding resin during possible exposures to high temperatures.